The utilization of renewable natural energy can be said without exaggeration to be a global issue. The technical problems of hydroelectric power, windpower, solar power, geothermal power, biomass power, etc. are being solved to enable these forms of energy to be actively used throughout the world. However, there are still large technical issues in use of the natural energy of the sea—which is the most promising. There are still few examples where this has been realized. Among these, many attempts have been made in the world relating to tidal power generation, but no universally applicable technology has yet been reported. In tidal power generation, in Japan's case, due to the distribution of tidal currents and water depths, it is necessary to limit the regions in which tidal generation facilities are set and select the drive structure system. The faster the tidal current, the better, but there are few regions where 3 knots or more can be expected. Regions of 2 knots to 1 knot in range are widely distributed from the Seto Inland Sea to the island of Kyushu. The water depth is also shallow at 40 m or so or less. These regions are also close to the land. If considering the drive structure of tidal power generation suitable for such regions, these would be advantageous in terms of fabrication costs and operating costs as well. Wide adaptation and use could be expected.
Regarding the drive structure of tidal current power generation apparatuses as well, the windmill propeller system, boat propeller system, Darrieus turbine wheel system, Sabonius turbine wheel system, etc. and also the fixed blade, crossflow, twisted blade, bucket conveyor system, and numerous other systems have been proposed. All of these have good points and bad points under the harsh ocean conditions and are in the trial stages. None have reached the commercial stage.
As the simplest structure with the smallest manufacturing cost, there is the ground-based waterwheel model which has been utilized from long in the past up to the present. However, if an overshot or undershot water wheel with a horizontal axis in an open path is laid flat and immersed in flowing water, it will not turn as it is. For this reason, water guide plates are used so that the water current is only applied to one side. By doing this, the wheel will turn. This is the crossflow system. Installation of water guide plates at the actual ocean flow, however, would be excessive in cost and impractical both with the fixed system and moving system.
As an improved waterwheel blade type power generation apparatus, PLT 1 discloses the following prior art. This prior art has a structure providing a plurality of blades equally over the entire circumference of a rotary body and providing fluid guide plates for guiding fluid so as to send the fluid to the fluid receiving parts of the blades. This prior art enables the blades to be raised by stopper parts within a predetermined range of angle and form fluid receiving parts. On the other hand, it enables the blades to be laid down at another range of angle. However, if this waterwheel blade type power generation apparatus were placed in the sea where the flow of fluid is reversed in flow direction or changed in direction, the fluid would not be able to be constantly guided to the fluid receiving parts and therefore power generation would become unstable.
On the other hand, PLT 2 discloses a windmill which is comprised of a rotary body around which are attached a plurality of vanes in a radial manner, which uses a gear mechanism to make part of the vanes perpendicular to the flow of air, and which makes the opposite side vanes parallel to the flow of air. However, the mechanism for adjustment of the mounting angle of the vanes of the prior art is complicated and breaks down due to the force acting on the vanes after long years of use. Long term stable operation is judged difficult. Furthermore, depending on this mechanism for adjustment of the mounting angle of the vanes, the energy loss is great and efficient power generation is judged difficult.
At the present time, development of a drive structure for the following such tidal current power generation apparatus meeting the conditions of the sea area covered, has been considered necessary. The conditions of the sea area are a tidal current speed of 2 knots to 1 knot and a depth of 40 m to 10 m or so. To handle changes in direction of the tidal current, simple structures not requiring special mechanisms, such as, crossflow water guide plates, propeller system turning mechanisms, and others, have been considered necessary. Further, it has been desired that (1) the power generation capacity should be one able to generate 100 kW, 500 kW, and further 1000 kW, 2000 kW, etc. for promotion of broad adaptation and use, and (2) the final power generation costs should be minimized, that is, the structure should be made simple so that the manufacturing costs become minimal, and changes in direction of tidal current should be handled to enable reliable power generation without requiring advanced technology and manufacturing precision.